Binocular Basics 1

This is the first post in a series that will review binocular basics for those interested. As you'd expect I'll start at the very beginning with very basic information. Throughout the series though the information will get more complex. Feel free to comment or question in the comments section below though.

Generally speaking, binoculars are manufactured in two basic designs in regard to prism assembly and structure. The first is a "porro prism" design which is easily recognized by shape. In a porro prism binocular the eyepiece or ocular lens assembly, is offset from the distal objective lens assembly. In most cases the objective lens will sit outside the eyepiece, although some manufacturers offer compact "reverse porro prism" designs where very small objective lenses nearly touch and are much closer together than the ocular.

I've superimposed the typical shape of a porro prism assembly in red lines above while the green dashed line shows the light path as it travels through the binocular. Note how the light enters the objective lens cell, passes into the upper prism, is reflected 2 times, passes into the lower prism block, bounces two more times and finally exits through the eyepiece.

Roof prism binoculars are quite different in structure and are generally favored for their superior ergonomics. In a roof prism binocular the ocular and objective lenses are lined up in a straight line (not off-set as in porro prism designs). Once again, I've drawn a rough roof prism assembly in red and the dashed, green line represents the path of light travel through the system.

As always, the light enters through the (typically larger) objective lens and travels up to the prism assembly. The assembly (in this case) is compromised of two glass blocks just as in the porro design at top. Unlike the porro however, a roof prism assembly reflects the light 5x. The area where the two blocks meet is called the "interface mirror", and this surface has to both reflect light at points and allow light to pass in others. It is very difficult to accomplish this without losing light through back reflection and/or refraction though, and the angles are more crucial than in simpler porro designs. As such, roof prism binoculars average more expensive than a comparable porro prism.

This higher price adds some very real advantages though to include: superior ergonomics, better waterproofing, and a higher impact resistance (again assuming a comparable level of manufacture and design). Roof prism binoculars generally offer better ergonomics through their slimmer design, as porro prism binoculars average bulkier due to the offset design.

Most porro designs utilize a moving external bridge (see above) that slides the oculars in and out to achieve focus. Once again, this is a simpler and cheaper manufacturing design, however it suffers from one predictable flaw. As these tubes slide over top of one another you are continually wearing the seals that keep moisture out and inert gases in. Over time these will wear to the point of failure leading to moisture problems and internal fogging. In addition this external bridge is very susceptible to impact damage, leading to alignment problems as well.

In most roof prism binoculars the focusing system is internal. In the case of the Leica Ultravid above, internal "field collector lenses" move back and forth between the prism assembly and objective lens cell. Since this system is completely internal it is much more impact resistant, and since you are not constantly wearing the seals through abrasion the roof prism design maintains its water proofing & fog proofing.

Summary

As a final note, I need to qualify implications above. I've used words like generally & typically above and also used qualifying statements like, "assuming comparable quality". In most cases in optics the old adage, "You get what you pay for" is true to its word. In looking at binocular prices quickly online, I note full-sized porro prism binoculars (compacts excluded) range from just over $25 up to about $1,200 US. By comparison roof prism prices ranged from about $50 on up to nearly $3,000 US. Assuming less expensive binoculars are created by cutting costs on raw materials (quality of components), manufacturing costs (quality of construction), & labor costs, I certainly expect that a $1,200 dollar porro prism would out-perform a $100 roof prism in every way. However, if we compared the highest quality premium roof prism versus the highest priced porro prism, I'm certain most users would prefer and gravitate toward the roof prism. I say this from my own personal preferences, my experiences of meeting and birding with thousands of birders annually (and noting what binoculars they are using), and from my knowledge of the many independent reviews that have appeared in industry articles in varying popular publications. All suggest roof prism designs are favored across the board by most users.

Digiscoping basics 3 - selecting an adapter

crazed digiscoper lines up on a distant subject! ;p

No spotting scope has ever been developed with use of a digital point & shoot camera in mind. Conversely, no small p&s camera has ever been designed to couple with a spotting scope; these smaller p&s are generally designed for the masses with close range portraiture and scenic shots in mind (perhaps even a bit of macro for fun). However, through trial & error we've discovered that these two items can indeed be used together to achieve amazing images!

Since neither piece was designed with the other in mind, it has been left to inventive individuals to craft devices to couple cameras & scopes effectively. In the early days of digiscoping experimentation this was done with soda bottles, PVC plumbing fittings, balsa wood, & lots of duct tape. Some designs worked quite well, while others.... well...

Today, digiscoping is a bit more user friendly as major optics manufacturers have recognized digiscoping potential and popularity and most have added at least one branded adapter for use with their products (often more). You can also find a wide array of aftermarket products designed for universal application on many camera and scope models.

generic platform style adapter

The piece above is representative of a fairly standard example of aftermarket, universal digiscoping adapter. It utilizes a vice clamp that tightens onto the spotting scope eyepiece, so it can be used on nearly any scope. The plastic platform accommodates nearly any digiscoping cameras via the 1/4"x20 threaded tripod mount (found on the bottom of the camera). The mounting platform is slotted on two sides so cameras with center, left, or right side tripod mounts can be used. It has separate controls to adjust the height of the platform, and another that moves from side to side allowing you to get the camera properly centered behind the scope. The slots also allow you to adjust for the proper distance between the eyepiece and the camera lens as well.

These adapters are a great alternative for older scope models, or scopes without a manufacturer's branded solution. They are also great for digiscoping experimentation due to their comparatively inexpensive price points. However, as with any design there are drawbacks as well. Generally speaking, a more universal (versatile) adapter that accommodates many scopes and cameras, requires a greater range of adjustment making the piece more complex, and larger in size & weight.

These "platform-style" universal adapters generally suffer from repeatability issues as well, because they have so many moving parts, they often aren't mounted in the same spot on the eyepiece, and because (as with all platform style adapters) the camera is prone to turning on its axis. Their larger comparative size make these more difficult to carry. While I would rate these as the least user friendly option available, sometimes with off-brand or old model scopes they may be the only option.

generic "screw-thread" universal adapter

Most early cameras had filter thread rings (or threaded accessory adapters) on the end of the camera lens. As such, one of the most common early adapter styles (and still one of the most popular) is the threaded tubular mount adapter. The model above is an example of the earliest style, which was designed for all scopes. To accommodate many eyepiece widths the tube was over sized to fit over even the widest of eyepieces. Here again, the universal application led to difficulties in use. You were required to use three different set screws to fill the gap left between the eyepiece and the inner wall of the over sized adapter. While a great idea in theory, in practice this was time consuming and it was difficult to get the camera centered as tightening one screw often moved the camera back out of center. For stationary subjects where time was no issue this is not a huge disadvantage, but many wildlife images were missed while still fighting to get the camera centered.

Driven by consumer demand, the next generation of tubular adapters were machined to fit specific eyepiece widths. Unlike their universal predecessors, these improved tubular designs (similar to the NEW Leica digital adapter 4 at bottom) fit a specific eyepiece perfectly, slipped on quickly, and the camera was always centered. These adapters have been the choice of many digiscoper in the years since due to their simplicity, compact size, and mounting speed.

Unfortunately, in recent years most digital p&s camera models have discontinued offering accessories, and now there are almost no p&s cameras offer filter threads (maybe 2 or 3 in a field of hundreds). As such, individuals wanting to digiscope with these adapters were forced to seek out a single specific camera model or two. They are now very restrictive as a result. This design can also offer problems as you stack adapters and threaded bushings to connect the camera to the threaded adapter, because the camera lens can be too far from the eyepiece to work to its full potential (see effects of this in post "digiscoping basics 2 - lining up the camera").

Leica digital adapter 2 adapter

In 2006 Leica introduced its unique digital adapter 2. This design took advantage of the mounting speed of the popular tubular design, but featured a revolutionary clamp design allowing use of nearly any digiscoping p&s camera! Two rubber-padded clamp jaws could be adjusted to hold a smaller digital p&s, camera phone and even some smaller video cams in place without dependence on threads. This opened the field to hundreds of camera models.

As with other designs though this increased versatility and compatibility does make the piece a bit larger. The Leica digital adapter 2 (DA2) was machined exclusively to the diameter of the Leica 20-60x zoom, 20x wide-angle, and 32x wide-angle eyepieces, but not other brands. Some of the "tinkerers" in the market were able to adapt this to some other eyepieces with smaller diameters, but again this took a bit of creativity to shim the excess space evenly.

revolutionary Leica digital adapter 2 with unique clamp design

In January 2009, Leica brought the new 82 mm Televid spotting scope to the marketplace featuring the first wide-angle zoom eyepiece ever developed. The wide-angle 25-50x zoom eyepiece was both taller and wider than Leica's previous eyepiece models so the digital adapter 2 would not fit over this.

Leica digital adapter3, APO Televid 82 mm spotting scope, & C-Lux camera

Leica introduced the new digital adapter 3 in January of this year. This piece is similar in design to the DA2, but utilizes a unique twist-lock connector at it's base and increased adjustment to accommodate all of the Leica eyepieces from the shorter, thinner former 20x to the largest of the line the new 25-50x wide angle. As such it also will mount to other brand spotting scopes to include many Kowa, Swarovski, Zeiss, & other models with an eyepiece diameter between 53 - 68mm.

Leica digital adapter 3

The digital adapter 3's unique twist-lock, tightens evenly from all sides insuring the camera is instantly centered on many eyepieces, and it incorporates a mechanical cable release arm (see second image up). Since this versatile adapter can be adjusted to accommodate so many eyepieces and cameras, it also appears somewhat complex and is larger (and more expensive) than its predecessor.

Leica digital adapter 4 prototype

However, never fear, for those who prefer simplicity there are options as well. In late summer 2009, Leica will introduce a VERY simplistic option when they introduce the new digital adapter 4. The new DA4 will be machined precisely to the diameter of the 25-50x wide angle eyepiece and will mount directly to only one camera model - the Leica D-Lux 4. By making this piece an exclusive mount for only one camera on a single eyepiece model, you have no need for additional adjustments resulting in a very compact and simplistic adapter.

So if you are wanting to mount a variety of cameras on varying eyepieces or if you simply want to slide the camera on and push the button, the new Leica line-up will offer solutions for all.

Digiscoping basics 2 - Lining up the camera

"American Green-winged Teal" digiscoped Arcata, CA 4/2009

When coupling a small digital point & shoot (p&s) camera behind a scope with a zoom eyepiece you will always see some sort of vignetted dark circle around the subject. As I've stated previously this is not a big issue and it typically disappears when you increase your camera zoom. Fixed wide-angle eyepieces will often not show this vignetting, but like most scope users I prefer the versatility of the zoom.

I actually like to use this circle to tell if my camera is centered properly over the eyepiece. When centered, the blackened sections of the image will appear uniform on either side of the screen and look the same at top & bottom.

If not centered properly, the vignette will disappear from one edge but not the opposite (as above) or perhaps from all but one corner of the image as you increase scope zoom. This is a clear indicator that your camera is off center. In the example shown above, the camera is a bit too far to the right and needs to be adjusted slightly to the left for best results. Remember, that the circle we are working with is less than 4 mm wide so adjustments will be slight. These seemingly small differences will become even more problematic as you increase the scope zoom because the small circle of light leaving the eyepiece (exit pupil) may be reduced from 1/2 to 1/3 its original size when you increase the scope zoom.

With our 2 dimensional adjustments made on the flat plane from side to side, up & down, and on the diagonals, we now need to turn our attention to getting the proper distance between the camera lens and the scope eyepiece.

old style, generic universal digiscoping adapter

This last adjustment seems to be the one most commonly ignored or missed in many digiscoping set ups resulting in ruined photos and great frustration. In many older, well established digiscoping websites, you may find this is largely ignored, not mentioned, or may seem unnecessary or not understood by many long time digiscopers due to inherent biases of certain types of formerly popular adapters.

The sample universal adapter above is fairly typical of most early adapters that utilized filter-thread (accessory) rings on the front of the p&s cameras as a means of attachment between the camera and adapter. Unfortunately, there are almost no current p&s models that still offer accessory threads because these units are replaced so frequently that accessories really don't seem to sell. It seems each year there maybe 2 in a field of hundreds of new digital p&s cameras that both lend themselves to digiscoping and offer filter thread rings at the front of the lens. These adapters are extremely limited as a result.

Another issue with these adapters is that due to the metal rings and adapter rings present between the two lenses these adapters almost invariably meant you could never get the two lenses too close together. As a result, many sites erringly suggest you always need to get the lenses as close as possible together for best results.

blackened, semicircular arcs appear when lenses are too close together

If you get your eye too close to a binocular lens you will get "black out" sections in your view that appear as shadowed arcs near one side of the image as seen in the image above. You don't have to take my word for it, try it for yourself. twist or roll down the eyecups on your binoculars and remove your glasses if you wear them and get the binocular eyepieces as close as possible to your eyes. You should note an effect similar to what is shown above.

Well not surprisingly, the effect is the same when coupling two lenses afocally (that is mounting a camera with a lens behind an eyepiece in this case). If the two lenses are too close together, you need to draw these apart until you see a more uniform colored background. This is particularly noticeable on light backgrounds like the sky.

when lenses are too far apart you'll note darkened corners

In the image above I've purposely pulled the lenses too far apart. If you experiment with your eye and a binocular or scope you can actually predict what happens in digiscoping as the systems really aren't too terribly different. When you move your eye away from the lens, your field of view collapses leaving just a small circle of light visible. You can see this happening in the image above as well. As the lenses are drawn apart the field begins to collapse and you begin to see shadowing at each corner of your image.

Note the difference in the terms "shadowing/shadowed edge" versus "vignetting/vignetted edge", I differentiate between these two as they indicate a different problem. As I define these terms "shadowed edges" have a bit of opacity to them - that is you can see through them a bit. A "vignetted edge" is sharply defined and completely black with no opacity.

A sharply defined blackened edge or vignette indicates you are off center or simply need to run your zoom out more. Shadowed edges generally indicate the two lenses are too far apart and need to be moved closer together. Shadowed arcs that are in the interior of the frame will have a lighter section between the shadow and the edge. When seen you should move the two lenses a bit further apart.

Not the most interesting subject I realize but to save time, I just zipped out the back door and took some sample shots of my storage shed. The light doors provided a good background to show shadowing. When the lenses are adjusted properly the field should look uniform and be devoid of shadowing & vignetting.

As I travel the country and beyond teaching digiscoping classes, I find that coupling errors are responsible for a majority of common digiscoping image problems/failures. Hopefully some will find this information helpful. As always, if there are ever any questions feel free to ask in the comments section. I'll happily address all to the best of my ability.

J